1. Field of the Invention:
The present invention relates to a semiconductor device having a waveguide thereon.
2. Description of Prior Art:
Hitherto, a semiconductor devices having a waveguide thereon are widely manufactured. As one exemplary embodiment of such conventional semiconductor device, a laser is shown in FIG. 1 wherein the following epitaxial growth layers are formed on
a semiconductor substrate 1 having strip shaped groove 1' of n-GaAs: PA0 a semiconductor substrate 101 having a step 101' n-GaAs:
a first clad layer 2 of n-Ga.sub.l-x Al.sub.x As, PA1 an active layer 3 of non-doped Ga.sub.1-y Al.sub.y As, PA1 a second clad layer 4 of p-Ga.sub.1-x Al.sub.x As, and PA1 a current limiting layer 5 of n-GaAs. PA1 a first clad layer 2' of n-Ga.sub.1-y Al.sub.y As, PA1 an active layer 3' of n- or p-Ga.sub.1-x Al.sub.x As, PA1 a second clad layer 4' of p-Ga.sub.1-y Al.sub.y As, and PA1 a current limiting layer 5' of n-GaAs.
A strip shaped current injection region 6 is formed by Zn-diffusion from the surface of the current limiting layer 5 at a part above the groove 1'. A p-side ohmic electrode 7 and an n-side ohmic electrode 8 are formed on the current limiting layer 5 and on the bottom face of the substrate 1, respectively. By taking the above-mentioned configuration, the laser oscillates in the active layer 3, and the oscillated light is confined in the strip region defined above the groove 1' since the region has higher effective refractive index than other parts of the active layer 3. The light is emitted from both end faces of the active layer 3 in the direction perpendicular to the sheet of FIG. 1, with its plane of polarization parallel to the direction of the plane of the active layer 3. Accordingly, stable transverse mode oscillation is obtainable.
Some of the inventors proposed terraced substrate type lasers, and its one exemplary configuration is shown in FIG. 2 which was disclosed in the Japanese Patent non-examined publication No. Sho 56-110285 published Sept. 1, 1981 (Japanese Patent Application No. Sho 55-13159) which corresponds to a part of the disclosure of the U.S. patent application of Itoc et al. Ser. No. 224,821 filed on Jan. 13th, 1981, Pat. No. 4,392,227.
In the terraced substrate type laser the following epitaxial growth layers are formed on
A strip shaped current injection region 6' is formed by Zn-diffusion from the surface of the current limiting layer 5' at a part above an oblique region 31' of the active layer 3' formed near and above the step 101'. A p-side ohmic electrode 7 and an n-side ohmic electrode 8 are formed on the current limiting layer 5' and on the bottom face of the substrate 1', respectively. By taking the above-mentioned configuration, the laser oscillates in the active layer 3' and the oscillated light is confined in the lasing region 31' defined above the triangular thick part of the first clad layer 2', since the lasing region 31' has a higher effective refractive index than other parts of the active layer 3'. Therefore, the oscillation light is emitted from both end faces of the lasing region 31' in the direction perpendicular to the plane of sheet of FIG. 2, with its plane of polarization parallel to the direction of the oblique lasing region 31'.
In both above-mentioned conventional embodiments, the active regions are strip shaped, that is, they have parallel boundaries in the active layer 3 or 3', accordingly, both ends of the active region or the cavity have substantially the same configuration each other.